This invention relates to embossing rolls or engraved rolls for embossing tissue or plastic film or other webs. More particularly, the invention relates to removable embossing plates which can be interchanged without creating pattern discontinuity at the plate edges (possibly by patterning the plates identically) so a few spare plates make it possible to replace any plate on the roll, again without causing pattern discontinuity.
Paper products such as bathroom tissue and kitchen towels are commonly formed on a rewinder line in which one or more jumbo rolls of webs are unwound, perforated, and rewound into retail sized rolls. Many rewinder lines include an embosser for forming embossments in one or more webs and perhaps a glue deck to bond webs together.
Co-owned U.S. patent application Ser. No. 10/153,335, filed May 2, 2002, now U.S. Pat. No. 6,716,017, and PCT Publication WO 02/072340 describe an embossing roll with removable embossing plates. Current commercial practice of providing an embossing roll with removable plates involves engraving an embossing pattern onto a set of removable plates, which cover the embossing roll.
Beidel U.S. Pat. No. 3,673,839 describes an embossing roll made of identically patterned rings or short cylinders. One sphere ring or cylinder can repair any damaged piece. Beidel does not describe circumferentially divided plates, i.e., plates which do not extend around the entire circumference of an embossing roll so that any circumference of the roll includes at least two plates.
Embossing plates for covering a roll tend to be mechanically identical, (i.e., identical in dimensions and in placement of locking features), which means they could be physically interchanged, i.e. installed without regard to original order. However, since the original patterning typically was not commensurate with the plate dimensions, the various plate boundaries ‘cut’ the overall pattern at different pattern features. In consequence the plates, while largely identical physically, were each patterned differently, in the sense that the pattern features located at each edge or corner were different from plate to plate. This meant the plates could not be interchanged without creating pattern discontinuities where they abutted their new neighbors. They therefore had to be installed in a very specific arrangement.
This non-interchangeability meant that if a user wished to maintain spare patterned plates to repair potential future damage, he had to stock an entire replacement plate set. When ordering a replacement plate, great care had to be exercised to determine just how the patterning should be aligned to that specific plate destined for that specific location.
Although plates covering a roll tend to be dimensionally identical, exceptions may occur at the ends of the embossing rolls. When fixed-width plates are used to cover an arbitrary roll (rather than scaling the plates to fit the roll), the number of plates and the width of the last plate is determined by the required overall face width of the embossing roll. At one end of the roll, row-tiling may begin with either a full-length plate or a special half-length plate (with a shifted locking feature). At the other end, row-tiling is terminated by a normal plate that is cut to a length somewhere between a half and a full-length plate, and which may also have its locking features displaced. This dimensional or locking features distinction between plates for different locations is another handicap when preparing for future damage, or when ordering a replacement plate.